Well, you may as well ask why Janeway didn't make herself an Admiral. They really weren't in Starfleet's normal operations sphere anymore so there really wasn't much point to promoting Kim. He was already part of the Senior Officers group in the first place (which for someone out of the Academy, was a pretty big thing).

And the reason why modern Navies have a "Get promoted or retire" mentality is because in Modern Navies room for officers is limited because said Armed Forces are limited to Earth. They only have so many ships and so many people going in and out.

With Starfleet, they have all that vastness of space and new ships being built all the time so there's no need for that limitation anymore because there's always more room. So there's no real problem with not getting promoted once every few years.

It's been awhile since I've seen VOY, but I'm hard-pressed to recall anything particularly outstanding that Kim did as well. Possibly his contributions to Astrometrics and his work to get the Hirogen off the ship in Killing Game?

Unfortunately, I could also make up a list of dumb things he did, sooooo....

With a few rare exceptions... I doubt very many people at all got promoted on that trip. You have a single ship, with a single command structure and promoting people is just gonna screw with that. There's even less of a need for promoting people as you take casualties for the most part.

Tuvok got promoted, but that was mainly to cement him as third in command more than anything else. Tom lost rank, the Voyager hierarchy wasn't effected... at all. He got it back, and the only consequence was Harry feeling deprived.

Now after Endgame, I'm sure there were promotions across the board. Pity they decided to fade to black rather than show an actual resolution.

Regarding the question about Paris getting promoted but not Kim....as i recall, didn't Janeway (having accepted their plight of being stuck in the delta quadrant) give Paris his rank because that was the rank he had achieved in Starfleet prior to his criminal indiscretions

And so she basically decided, in view of their predicament, to restore people to their previous positions or previous trained abilities (so Chakotay became first officer and the Maquis that had previously served with Starfleet were given the ranks that they had once originally earned)

So Tom was a part of that decision....and he wasn't promoted while Kim wasn't.....just simply restored